ARM: dts: Migrate U-boot nodes to U-boot DT files for stm32h7

In order to prepare and ease future DT synchronization with kernel
DT, migrate all U-boot specific nodes/properties/addons to
U-boot DT files.

As sdmmc is not yet supported on kernel side, sdmmc nodes
are located in eval-u-boot and disco-u-boot DT files.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>